Merge pull request #3952 from Homebrew/revert-3911-misfeature

Revert "build: do not skip runtime deps of buildtime deps"

Author: ilovezfs

Library/Homebrew/build.rb

@@ -59,6 +59,8 @@ def expand_deps
         Dependency.prune
       elsif dep.build? && dependent != formula
         Dependency.prune
+      elsif dep.build?
+        Dependency.keep_but_prune_recursive_deps
       end
     end
   end